Abstract

Mucocele-like tumor (MLT) of the breast is histologically characterized as mucin-containing cysts with mucin leaking to the stroma. MLT is known to accompany atypical epithelium and ductal carcinoma in situ (DCIS). We report here a case of MLT of the breast including atypical epithelium and DCIS. In addition, floating cellular clumps with irregular nuclei were observed. Thus, the MLT was regarded to include mucinous carcinoma in early stage. It is assumed that detachment of cells from the atypical epithelium including DCIS is a possible onset for the development of mucinous carcinoma. In this case, focal invasive tubular carcinoma with features of the predominance of open tubules composed of a single layer of epithelial cells was identified. No myoepithelial cells were confirmed by immunostaining of p63 or DC10 in the neoplastic cells. Pathological features and significance of this rare case are described.